Concentration by continuous flash evaporation

ABSTRACT

In the embodiments of the invention described herein, a liquid such as gelatin or an egg constituent having heat degradation or fouling tendencies is concentrated by passing it through a platetype heater while maintaining sufficient pressure to prevent boiling and keeping the temperature of the liquid below the temperature at which the liquid thermally degrades or tends to foul the heating surfaces. The heated liquid is thereafter passed through an unheated portion of the plate heater at reduced pressure, allowing vapor to form, and creating a homogeneous mixture of concentrated liquid and vapor. The concentrated liquid is extracted in a separator, and in the case of egg, may be frozen or spray dried.

United States Patent Bain et al.

[451 Apr.18,1972

CONCENTRATION BY CONTINUOUS FLASH EVAPORATION 3,469,617 Palmason ..159/47 2,467,769 4/1949 Morrow et a1. 159/2 X 2,572,857 10/1951 Hall et a1 159/2 X 2,853,127 9/1958 Sessen 159/2 X 3,073,380 I/ l 963 Palmason ..159/49 3,170,804 2/1965 Kline et a1 ..99/210 3,113,872 12/1963 Jones et al ..99/210 X 3,345,182 10/1967 l-luste ..99/71 3,431,655 3/1969 Grover et a1 ..34/5 1,562,309 Ill 1925 Dickerson ..99/155 Primary Examiner-Norman Yudkofi Assistant Examiner-J. Sofer [30] 110mg Application Prim'ny Dam Au0rney-Brumbaugh, Graves, Donohue & Raymond Ma 6, 1969 Great Britain ..23,135/69 y 57 ABSTRACT [52] US. Cl ..159/47, 159/2, 159/28, In the embodiments ofthe invention described herein a liquid 159/ 99/199 99/210 99/196 such as gelatin or an egg constituent having heat degradation [51] Cl "Bold 1,28 Bold 1/ 2 A231) or fouling tendencies is concentrated by passing it through a figg ggg gf plate-type heater while maintaining sufficient pressure to [58] new Search 99 1 5 prevent boiling and ,keeping the temperature of the liquid below the temperature at which the liquid thermally degrades 56 R f d or tends to foul the heating surfaces. The heated liquid is 1 1 e erences thereafter passed through an unheated portion of the plate UNITED STATES PATENTS heater at reduced pressure, allowing vapor to form, and creatmg a homogeneous mixture of concentrated liquid and vapor. 2 1 6/1955 Bassett et R The concentrated liquid is extracted in a separator, and in the I Dahlstedt n n. R X case ofegg may be frozen or pray dried 3,195,613 7/1965 Hawkins ..159/2 R X 3,453,184 7/1969 Gemassmer et al ..159/47 R 10 Claims, 2 Drawing Figures {HOT WATER IN /7 ,ZZ DRIED PRODUCT /7 /5 I FEED 1N E C; 1 ,FLAsHER Z? EAT 0 HOT WATER our 1 /4 UNH E ---Psooucr our a, 24 4 4 z/ 8 z/ CONCENTRATION BY commuous FLASH avxroaxrrorv BACKGROUND OF THE INVENTION The present invention relates to a method for producing concentrated materials which, because they contain proteins, lipids, etc., are subject to denaturation or thermal degradation when excessively heated. Such materials include gelatins, whole egg, egg albumen, egg yolk, and corn steep liquor. Concentration of these materials by removing water or other liquid constituents not only results in substantial savings in packaging, transportation and storage costs, but also in many cases improves the shelf life of the material, particularly when the concentrating process is concluded by spray or freeze drymg.

I-Ieretofore the concentration of the liquid materials has been carried out in varying designs of shell and tube-type evaporators or has utilized thermal syphon, forced circulation for rising and/or falling films, or agitated or wiped film princi' ples. Heat and flash principles have also been employed whereby liquids are concentrated by passing the heated liquid through a valve or constricted orifice, into a low pressure chamber to produce instantaneous flashing. With highly heatsensitive materials such as egg constituents, however, such processing usually produces localized overheating with subsequent denaturation and degradation of the material and fouling of the apparatus. Moreover, the relatively low heat transfer rates effected by such processing result in a long residence time within the evaporator and, hence, increased likelihood of degradation. With instantaneous flashing of heated liquid, the violent pressure let-down usually produces shear damage to sensitive materials such as egg constituents.

SUMMARY OF THE INVENTION In accordance with the invention, heat-sensitive liquids are concentrated by subjecting them to a controlled tortuous path heat and continuous flash evaporation process which achieves the desired degree of concentration without the normally accompanying adverse effects upon the liquid. Initially, the liquid is passed through a tortuous heated flow path while being kept under sufficient pressure to prevent any boiling within the confines of the heated path and at temperatures below that at which it thermally degrades. To avoid local overheating, the tortuous path induces turbulent flow to shorten the time during which any selected portion of the liquid is in contact with the heated path surfaces. The heated liquid is then passed into an unheated tortuous flow path which is designed to allow the pressure to drop relatively gradually below the vapor pressure of the liquid. Vapor is formed by continuous flashing and, due to the tortuous character of the flow path, the resulting concentrate, which may be quite viscous, is prevented from accumulating on the flow path surfaces. The concentrated liquid-vapor mixture then passes into a separator without sudden flashing.

BRIEF DESCRIPTION OF THE DRAWINGS concentration system in accordance with the invention; and

FIG. 2 is a schematic sectional view of one form of plate evaporator used in the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the typical heat and flash concentration system shown schematically in FIG. 1, aheat-sensitive liquid to be concentrated, such as gelatine, egg albumen, egg yolk, whole egg, or corn steep liquor, is introduced through a feed line 11 and may be mixed with recycled liquid in a line 12 in which it is carried to an evaporator 13. The evaporator 13 is preferably of the plate type illustrated in FIG. 2 to provide turbulent flow characteristics, although other turbulent flow-type evaporators may be used.

In the evaporator shown in FIG. 2, a plurality of adjacent thin corrugated metal plates 14 are held in spaced relation by intervening gaskets 15 to form a series of parallel passes 16 for the feed liquid and intervening passes 17 for a heating fluid such as hot water. The evaporator structure, which may be of the same general type described in the Palmason US. Pat. No. 3,073,380, is easily disassembled for the insertion or removal of plates and, by providing internal portals 18 at suitable locations and suitably arranging the gaskets 15, any desired pass configuration can be formed. The heating fluid is supplied through an inlet pipe 19, passes in parallel through the interspaces 17 in a heated portion A of the evaporator and emerges through an outlet pipe 20. Water is the preferred heating fluid because its temperature is easily controlled so as to prevent the liquid to be concentrated from reaching a temperature in excess of its temperature of thermal degradation. For example, whole egg or egg yolk will thermally degrade above about 145 F. and egg albumen will degrade above about F. Certain heat-sensitive liquids, however, can tolerate higher temperatures and thus may even permit the use of steam as a heating fluid.

After passing through the heated portion A of the evaporator, the material enters an unheated portion B in which the plates 14 are arranged in a similar manner to provide three adjacent tortuous flow material passes 21 but no heating fluid is applied to the intervening space 22. The arrangement depicted in FIG. 2 is designated as a 2-2-3P configuration, having two parallel downwardly directed heated passes 16 followed by two parallel upwardly directed heated passes 16 and thence three downwardly directed unheated passes 21, the P designation indicating the unheated characteristic of the last three passes.

Referring back to FIG. l, the homogeneous liquid-vapor mixture from the evaporator section B enters a line 24 at high velocity and is directed to a separator 25 where the vapor is separated from the concentrated liquid and is drawn off through a line 26 to a condenser 27. There it is condensed to the liquid phase and pumped through line 25$ and out of the system. The concentrated liquid product in the bottom of the separator enters a product line 29 and may be removed from the system through an outlet line 30. If a greater degree of concentration is desired, a portion of the concentrated product is recycled by passing it through a line 31 so that it mixes with the feed material in the line 12. By controlling the proportion of product which is recycled, the concentration of the feed material may be adjusted and, hence, the concentration of the product at the outlet 30.

The concentrated product at the outlet 30 may have a total solids content of, for example, l0 to 70 percent, whereas the total solids content of the feed material may be, for example, from 5 to 55 percent. If the concentrated material, such as egg, must be kept at room temperature, it is preferably passed through a conventional spray or freeze dryer 32 to produce a substantially dry concentrated egg product which has improved shelf life and minimum loss of quality.

If the concentrated product can be maintained and marketed at at a low temperature, it is applied to a conventional freezer 33 to produce a frozen concentrate. Egg constituents processed in this manner have substantially improved shelf life with no appreciable loss of quality. Thus, the present invention provides a new egg product which is both frozen and concentrated, as opposed to the presently available frozen unconcentrated egg products. The ultimate user of the concentrated product will find it to be more convenient and economical than the same product in the unconcentrated form. For example, the frozen concentrated egg product thaws out much faster and more uniformly than the frozen unconcentrated egg, resulting in easier handling and less chance of product loss. Furthermore, when reconstituted either directly or by water from a recipe which includes water, the concentrated egg imparts the same characteristics as fresh whole egg.

In the evaporator 13, the plates 14 are preferably corrugated so as to assure maximum turbulence of the liqu d in the heated portion of the flow path. This turbulence increases the rate of heat exchange and ensures that no liquid particle will be in contact with the heated plate surfaces for an excessive length of time. The extremely short contact time of the liquid with the heated plates is important since such liquids as eg albumen will thermally degrade if heated above their critical temperature for even an instant. Similarly, the feed rate and heating fluid temperature must be controlled so that the temperature of the liquid is not permitted to exceed its particular temperature of degradation.

The plate spacing and pass arrangement of the evaporator 13 are selected so that the liquid pressure in the heated portion A of the evaporator is greater than the vapor pressure of the liquid at the end of the last heated pass, thereby preventing any boiling of the liquid in the heated portion. Preferably the pressure in the heated portion is at least about 1.0 psia. Unlike previously known heat and flash evaporators, the evaporator according to the invention does not utilize a valve or constricted orifice to maintain pressure in the heated passes. Rather, it has been found that the unheated plate passes 21 will allow a relatively gradual pressure drop which, in turn, results in the maintenance of adequate pressure within the heated passes and at the same time permits relatively gradual continuous vaporization of the liquid from the material in the unheated passes. The necessity of a continual pressure drop in the unheated portion B of the evaporator requires that the separator 25 by maintained under vacuum conditions relative to the pressure at the end of the heated portion A. The greater the difference between the pressures at the end of the last heated pass 16 and that in the separator 25 the greater the degree of evaporation that will occur in the unheated passes 19. For this reason, it is preferred that the pressure in the separator be subatmospheric.

It will be noted that the unheated portion B of the evaporator is designed similarly to the heated portion A in that closely spaced corrugated plates 14 are utilized. As was the case with the heated path, highly turbulent flow is induced. As the heated liquid proceeds through the unheated path, the pressure continually diminishes, causing vapor to form by flashing. The formation of the vapor increases the volume of the throughput and thus causes its rapid acceleration. Even more turbulence results, creating a homogeneous liquid-vapor mixture. Because a pressure gradient may occur between the end of the unheated zone B and the separator, it is apparent that some vaporization will also take place in the line 24 which connects the evaporator 13 to the separator 25.

The turbulent flow of the liquid-vapor mixture is especially beneficial in that, as vapor is evolved, the liquid portion of the mixture becomes more and more concentrated and, with products such as gelatin, very viscous. Were it not for the turbulent flow feature of the invention, the highly viscous concentrate could foul the evaporator, necessitating frequent cleaning and causing product loss. With the arrangement of the present invention, however, the interval between cleaning operations for evaporators processing such materials is greatly increased.

The above described process may be typically utilized to concentrate gelatin from about to 20 percent total solids up to about 20 to 50 percent total solids. While egg albumen has a natural total solids content of from 11.5 to 12.5 percent, processing or handling prior to concentration may cause significant departures from this range. Thus it may be said that egg albumen may be concentrated according to the invention from about 5 to 20 percent T.S. (Total Solids) up to about 20 to 40 percent T.S. Similarly, whole egg (natural T.S. 25 to 27 percent) may be concentrated from to 35 percent T.S. up to about 40 to 55 percent T.S. and egg yolk (natural T.S. 43 to 44 percent) from 35 to 55 percent T.S. up to about 55 to 65 percent and possibly as high as 70 percent T.S.

The following examples are representative of the method of this invention.

EXAMPLE 1 A high bloom gelatine was concentrated according to the invention. No loss of gel power was detectable in the product and, despite the high viscosity of the product, no fouling of the evaporator surfaces occurred. The conditions of the test were as follows:

Plate Arrangement 66-6P Vacuum, lnches of Hg (in separator) 26 Temperature of Heating Water 230F. Feed Rate, lbs. per hour 230 Feed Concentration, T.S. 20 Feed Pressure, psig 60 Recycle Rate, lbs. per hour 1,500 Condensate Rate, lbs. per hour Product Rate, lbs. per hour Product Concentration, T.S. 35 Product Temperature (in Separator) 125F. Product Viscosity, Centipoise 0 l25F. l2,000-l5,000

EXAMPLE 2 Liquid whole egg was concentrated according to the invention without any loss in the quality of the product and without any fouling of the evaporator. The following is a summary of the trial run data:

Plate Arrangement 4-4-44! Vacuum, lnches of Hg (in separator) 28.5 Temperature of Heating Water l40F. Feed Rate, lbs. per hour 220 Feed Temperature 50F. Feed Concentration, T.S 25 Feed Pressure, psig 70 Recycle Rate, lbs. per hour 2,900 Condensate Rate, lbs. per hour I00 Product Rate, lbs. per hour 120 Product Concentration, 70 T.S 46 Product Temperature (in Separator) 95F. Product Viscosity, Centipoise 0 95F. 200

EXAMPLE 3 Concentration of egg albumen was successfully carried out in a plate evaporator similar to that used in Example 2. Again no loss in product quality or fouling occurred. The following data describes the conditions of the test run:

Plate arrangement 4-4-4-3P Vacuum, lnches of Hg (in separator) 28.5 Temperature of Heating Water I20F. Feed Rate, lbs. per hour 120 Feed Temperature 50F. Approx. Feed Concentration, T.S l2

Feed Pressure, psig 30 Recycle Rate, lbs. per hour 4,000 Condensate Rate, lbs. per hour 75 Product Rate, lbs. per hour 45 Product Concentration, T.S. 33 Product Temperature (in Separator) 90F.

Product Viscosity, Centipoise 0 90F.

EXAMPLE 4 To the concentration process of Examples 2 and 3 may be added a freezing step to obtain a frozen concentrated egg product. The following is a typical procedure:

Liquid whole egg, albumen or egg yolk is obtained from fresh eggs in the usual manner and, after screening to remove broken shell, it is chilled to 30 to 35 F. in a typical heat exchanger designed for this purpose. The chilled egg product may be briefly stored in enclosed stainless steel sanitary tanks.

Within the same day, the liquid whole egg, albumen or yolk is transported to a processing plant and uniformly blended. Any additives that may be desired, such as sucrose, corn syrup solids or emulsifiers are added at this time.

Pasteurization is then carried out in a suitable pasteurizer at F. for 3 minutes. The product discharging from the pasteurizer at 80 to 90 F. is fed directly into an evaporator according to the invention and concentrated under conditions such as are described in Examples 2 and 3. After concentration the product is fed directly to a chiller, e.g., a swept surface heat exchanger, where the temperature is reduced below 25 F. and preferably to to F. and the product is packaged in suitable containers. The packaged product is held at -30 F. for 8 to 24 hours for hardening and is stored thereafter at 0 F.

We claim:

1. A process for concentrating liquids comprising passing a liquid through a first heated tortuous flow path at a velocity sufficient to maintain turbulent flow therein, applying heat to the liquid therein, maintaining the pressure within said tortuous flow path high enough to prevent the liquid from vaporizing therein, directly thereafter passing the heated liquid into a second unheated tortuous flow path arranged to maintain turbulent flow and to allow the pressure therein to drop below the vapor pressure of the liquid, thereby flashing the liquid material in a relatively gradual and continuous manner while maintaining turbulence and forming a homogeneous liquid-vapor mixture therein, and finally separating the concentrated liquid and the vapor in a separator.

2. A process according to claim 1 wherein the tortuous flow paths are in a plate type evaporator and the liquid material is heated by circulating a heating fluid in indirect heat exchange relation with the liquid material only in the first tortuous flow path in the evaporator.

3. A process according to claim 1 wherein the separator is maintained at a pressure below the pressure at the end of the unheated flow path, without substantial instantaneous flashing in the separator.

4. A process according to claim 3 including the step of maintaining the separator at a pressure below atmospheric pressure.

5. A process according to claim 1 including the step of admixing a portion of the concentrated liquid from the separator with liquid to be concentrated and recycling the admixture so as to increase the concentration of the resulting product.

6. The process according to claim 1 wherein the liquid is selected from the group consisting of gelatin, liquid whole egg, egg albumen, egg yolk, and corn steep liquor.

7. In a process according to claim 1 wherein the liquid is an egg constituent having a total solids content of from about 5 to about 55 percent, heating the liquid to a maximum temperature no greater than about 145 F., maintaining said pressure in said first turbulent flow path at 1.0 psia therein to prevent the liquid from boiling, said liquid egg concentrate having a total solids content between about 20 and 70 percent.

8. A process according to claim 7 including the step of drying the egg concentrate to produce a dried egg product.

9. A. process according to claim 7 including the step of freezing the egg concentrate at a temperature below about 25 10. A frozen egg concentrate prepared according to the process of claim 9. V

Z gz g Q l V STAI ES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Dated April 18, 1972 lnvento'fls) Kenneth Lindsay Bain and Douglas Leslie Leonard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1 V l i w I Column 4, line 17, "Centipoise 0" should be -Ce'ntipo:i .se line 36 "Centipoise 0" should be -Centipoise C 7 line 55 "Centi'poise 0" should be ---Centipoise Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer v Commissioner of Patents 

1. A process for concentrating liquids comprising passing a liquid through a first heated tortuous flow path at a velocity sufficient to maintain turbulent flow therein, applying heat to the liquid therein, maintaining the pressure within said tortuous flow path high enough to prevent the liquid from vaporizing therein, directly thereafter passing the heated liquid into a second unheated tortuous flow path arranged to maintain turbulent flow and to allow the pressure therein to drop below the vapor pressure of the liquid, thereby flashing the liquid material in a relatively gradual and continuous manner while maintaining turbulence and forming a homogeneous liquid-vapor mixture therein, and finally separating the concentrated liquid and the vapor in a separator.
 2. A process aCcording to claim 1 wherein the tortuous flow paths are in a plate type evaporator and the liquid material is heated by circulating a heating fluid in indirect heat exchange relation with the liquid material only in the first tortuous flow path in the evaporator.
 3. A process according to claim 1 wherein the separator is maintained at a pressure below the pressure at the end of the unheated flow path, without substantial instantaneous flashing in the separator.
 4. A process according to claim 3 including the step of maintaining the separator at a pressure below atmospheric pressure.
 5. A process according to claim 1 including the step of admixing a portion of the concentrated liquid from the separator with liquid to be concentrated and recycling the admixture so as to increase the concentration of the resulting product.
 6. The process according to claim 1 wherein the liquid is selected from the group consisting of gelatin, liquid whole egg, egg albumen, egg yolk, and corn steep liquor.
 7. In a process according to claim 1 wherein the liquid is an egg constituent having a total solids content of from about 5 to about 55 percent, heating the liquid to a maximum temperature no greater than about 145* F., maintaining said pressure in said first turbulent flow path at 1.0 psia therein to prevent the liquid from boiling, said liquid egg concentrate having a total solids content between about 20 and 70 percent.
 8. A process according to claim 7 including the step of drying the egg concentrate to produce a dried egg product.
 9. A process according to claim 7 including the step of freezing the egg concentrate at a temperature below about 25* F.
 10. A frozen egg concentrate prepared according to the process of claim
 9. 